Fragment监听返回键

首先创建一个抽象类BackHandledFragment，该类有一个抽象方法onBackPressed()，所有BackHandledFragment的子类在onBackPressed方法中处理各自对Back事件的消费逻辑。onBackPressed返回布尔值，宿主FragmentActivity将会根据该方法的返回值判断子Fragment是否有消费Back事件。此外，宿主FragmentActivity还会保持一份当前Fragment的引用，当用户按下Back键时，宿主Activity会判断当前Fragment是否需要消费该事件，如果没有Fragment消费才会自己消费。

 public abstract class BackHandledFragment extends Fragment {

     protected BackHandledInterface mBackHandledInterface;

     /**
      * 所有继承BackHandledFragment的子类都将在这个方法中实现物理Back键按下后的逻辑
      * FragmentActivity捕捉到物理返回键点击事件后会首先询问Fragment是否消费该事件
      * 如果没有Fragment消息时FragmentActivity自己才会消费该事件
      */
     protected abstract boolean onBackPressed();

     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         if(!(getActivity() instanceof BackHandledInterface)){
             throw new ClassCastException("Hosting Activity must implement BackHandledInterface");
         }else{
             this.mBackHandledInterface = (BackHandledInterface)getActivity();
         }
     }

     @Override
     public void onStart() {
         super.onStart();
         //告诉FragmentActivity，当前Fragment在栈顶
         mBackHandledInterface.setSelectedFragment(this);
     }

 }

宿主FragmentActivity需要继承BackHandledIntegerface，子Fragment会通过该接口告诉宿主FragmentActivity自己是当前屏幕可见的Fragment。

 public interface BackHandledInterface {
     public abstract void setSelectedFragment(BackHandledFragment selectedFragment);
 }  

所以在Fragment的onCreate中会判断宿主FragmentActivity是否已继承了该接口。在Fragment的onStart()方法中就会调用该接口告诉宿主FragmentActivity自己是当前屏幕可见的Fragment。
宿主FragmentActivity就可以在onBackPressed()方法中对Back事件进行判断处理了。

 public class MainActivity extends FragmentActivity implements BackHandledInterface{  

     private BackHandledFragment mBackHandedFragment;
     private boolean hadIntercept;  

     @Override
     public void setSelectedFragment(BackHandledFragment selectedFragment) {
         this.mBackHandedFragment = selectedFragment;
     }  

     @Override
     public void onBackPressed() {
         if(mBackHandedFragment == null || !mBackHandedFragment.onBackPressed()){
             if(getSupportFragmentManager().getBackStackEntryCount() == 0){
                 super.onBackPressed();
             }else{
                 getSupportFragmentManager().popBackStack();
             }
         }
     }
 }  

DEMO完整下载地址：https://github.com/mxy1228/FragmentHandleBackDemo/

http://vinsol.com/blog/2014/10/01/handling-back-button-press-inside-fragments/